DEHYDRATED CULTURE MEDIA 47 



Bacto-S F Medium is recommended as a selective liquid medium for the detec- 

 tion of fecal streptococci from milk, water, swimming pools, sewage and feces. In 

 this medium coliform and other Gram-negative organisms are inhibited. Bacto-S 

 F Medium is prepared according to the formula of Hajna and Perry i. 



Sodium azide has been employed as a selective agent in media for the isolation 

 of streptococci by a number of investigators. Snyder and Lichstein^ and Lichstein 

 and Snyder^ reported that 0.01 per cent sodium azide in Blood Agar prevented 

 swarming of proteus and permitted the isolation of streptococci from stools and 

 other infected material without overgrowth by Gram-negative organisms. Mall- 

 mann* used 1:5000 sodium azide in a buffered Tryptose broth for the exami- 

 nation of sewage and reported that streptococci grew while coliform organisms 

 were inhibited. This method made possible an easy procedure for routine labora- 

 tory detection of streptococci. Packer^-^ used sodium azide and crystal violet 

 in the preparation of a selective Blood Agar for streptococci and Erysipelothrix 

 rhusiopathiae. Hajna and Perry^ devised a selective medium containing 0.05 per 

 cent sodium azide, dextrose and the indicator, brom cresol purple, for the detec- 

 tion of fecal streptococci in swimming pools, water samples and milk. They 

 specified 45.5 °C. as the incubation temperature, and reported that growth ac- 

 companied with an acid reaction, as shown by the change in color of the medium, 

 was almost complete evidence of the presence of fecal streptococci. 



To rehydrate the medium dissolve 36 grams Bacto-S F Medium in 1000 ml. 

 distilled water. Distribute in tubes and sterilize in the autoclave for 15 minutes 

 at 15 pounds pressure (121°G.). Final reaction of the medium will be pH 6.9. 



When the inoculum is greater than 1 ml., particular care must be taken to 

 preserve the correct concentration of the ingredients after dilution with the 

 sample. For example, if 10 ml. of water are to be added to 10 ml. of medium, 

 the medium should be prepared in double strength. 



One pound of Bacto-S F Medium will make 12.6 liters of medium. 



lAm. J. Pub. Health, 33:55o:i943- * Sewage Works J., 12:875:1940. 



3 J. Infectious Diseases, 67:113:1940. e j. Bact., 42:137:1941. 



•J. Bact., 42:653:1941. e J. Bact., 46:343:1943. 



BACTO 



B A G G BROTH (B442) 



DEHYDRATED 



Bacto-Tryptose 20 g. 



Bacto-Dextrose (Glucose) 5 g. 



Dipotassium Phosphate 4 g. 



Monopotassium Phosphate 1.5 g. 



Sodium Chloride 5 g. 



Sodium Azide 0.5 g. 



Bacto-Brom Cresol Purple 0.015 g. 



Bacto-B A G G Broth (Buffered Azide Glucose Glycerol Broth) is a selective 

 liquid medium for the detection of fecal streptococci from all types of specimens. 

 It is prepared according to the formula given by Hajna^ and is a modification of 

 SF Medium as described by Hajna and Perry. 2 Coliform and other Gram 

 negative organisms and buccal streptococci are inhibited on this medium as they 

 are on SF Medium while fecal streptococci develop unrestricted. 



In using SF Medium for the detection and isolation of fecal streptococci, 

 particularly Streptococcus fecalis, Hajna noted that acid production in the 

 medium was much more rapid when the inoculum consisted of a stool received 

 in buffered glycerol saline. Investigation of this observation showed that glycerol 



